Table of Contents
Introduction to top command
top program provides a dynamic real-time view of processes running in the Linux system. It also displays the system summary information and processes or threads currently managed by the Linux kernel. The output of the top command is interactive and can be controlled by pressing keys to some extent.
Understanding the output of top command
The top command output contains the three main sections: Summary Area, Fields/Columns Headers, and Task Area.
These are the Fields/Columns Headers, which you will see on the top command output.
- PID: It is the task's unique process ID.
- USER: It shows the owner of the tasks.
- PR: It is the priority of a task.
- NI: The nice value of a task. A negative value means higher priority, whereas a positive value means lower priority.
- VIRT: The total amount of virtual memory used by the task.
- RES: The non-swapped physical memory used by a task.
- SHR: The amount of shared memory used by a task.
- S: The process status of a task:
- D = uninterruptible sleep
- I = idle
- R = running
- S = sleeping
- T = stopped by job control signal
- t = stopped by debugger during trace
- Z = zombie
- %CPU: The percentage of CPU usage of a task.
- %MEM: The percentage of memory used by a task.
- TIME+: Total CPU time the task has used since it started.
- COMMAND: The command line which is used to start a task.
Different examples to use top command
Now, let's have a look at some practical examples of
top commands in the Linux system.
1. top command to display Linux processes
You can run
top command without any options or arguments to display running processes in the system. You can press q or kill the program to exit the output mode.
2. top command to display output in batch mode
-b option displays the output in batch mode or non-interactive mode. It will not accept any inputs and runs until you kill the program.
$ top -b
3. Set the delay time of screen updates in top command output
-d option allows you to specify the delay time between screen updates. It takes an argument of time in seconds as a number.
$ top -d num
For example, if you put the number 10 after
-d option, the output will be updated every 10 seconds. Try it on your terminal to get the desired output.
4. Set the number of iterations in top command output
-n option, you can put the limit of iterations top should produce in the output.
$ top -n num
For example, if to put the iterations limit of 5, you can use the following command.
$ top -n 5
5. Monitor specific process with top command
Instead of viewing all the processes, you can monitor the specific process using the process ID.
-p option lets you specify the process ID and view the particular process in the output.
$ top -p num
6. top command to display the process of specific user
Normally, top command displays the running processes of all users in the output. To view the process by specific users, you can use
-u option followed by the user name. You can also use user ID instead of the name.
$ top -u username
$ top -u userID
7. Adjust the output width of top command
-w option allows you to adjust the output width by decreasing it. You cannot increase the width of the output.
$ top -w num
8. Display Mem and Swap in KB/MB/GB/TB/PB/EB with top command
When top command is running, you can press
E option to change the unit of memory as displayed with top command. Different supported units are as shown below:
k - kibibytes -> top shows default in KB m - mebibytes -> Press E one time g - gibibytes -> Press E two time t - tebibytes -> Press E three time p - pebibytes -> Press E four time e - exbibytes -> Press E five time
By default top shows Memory and Swap in KB
When E pressed one time (show in MB):
When E pressed two time (show in GB):
Similarly you can press E multiple times to change the Unit type of Memory.
9. Sort Processes by Memory Usage in top command output
You can sort the process by memory usage in the output using
10. Sort Processes by CPU Usage in top command output
To sort the processes by CPU Usage, press
P at the displayed output.
11. Add or Remove Fields in top command output
f key lets you select or order fields in the output. When you press
f, the field management screen appears.
Select Field: Press 'd' or <Space> to select the field to display in the output.
Let's add the field UID to the output.
Then press 'q' or <Esc> to see the output.
Order Field: Navigate with Up/Dn, Right selects for move then <Enter> or Left to save changes
Now, let's order the field to a different location. Here, we are putting the field UID between USER and PR.
Press 'q' or <Esc> to see the output.
12. Hide the value 0 in top command output
You can press
0 to hide or show the value 0 in
top command output. The blank field in the output contains 0, which is suppressed.
13. Toggle Alternate Display Mode in top command output
You can use A to switch between alternate display or full display mode in the output. Next you can press 'g' where you will be prompted to enter a number between 1 and 4 designating the field group which should be made the current window.
14. Disable bold text in top command output
B key will disable or enable the bold text in the output. It alters both the summary area and task area for the current
window. As we can see, the bold texts are disabled in the output below.
Without pressing B
After pressing B
15. Change delay time in top command output
If you press
d, you will be prompted to enter the new delay time.
16. Change memory unit type in task windows
e, you can change the memory scale in the task window, which ranges from kibibytes (KiB) to pebibytes (PiB). If the scaling range is high, you are more likely to get zero value. Such zero values are not suppressed by interactive command
k - kibibytes -> top shows default in KB m - mebibytes -> Press e one time g - gibibytes -> Press e two time t - tebibytes -> Press e three time p - pebibytes -> Press e four time e - exbibytes -> Press e five time
Press e one time (show in MB):
Press e two times (show in GB):
Press e three times (show in TB):
17. Choose another window in top command output
When you press
g, you will be prompted to enter the number between 1 and 4 which allows you to choose another window or field group.
18. Display only active tasks with top command
You can view the active tasks in the system by pressing the key
i. Other idled or zombied processes will not be displayed.
19. Change colour mapping in top command output
You can press
Z key while top is running. After which you will be presented with the list of colors to choose with. Follow the instructions as shown below:
Here we will select 3 for yellow, and by default only Task Information is selected:
Accordingly you can choose between section 1 and section 2 and then press a to commit and add another combination. For example, here I have selected 4 = blue for S = Summary and then press a to commit and add another:
20. Scroll a window in top command output
You can use the following keys to scroll the tasks or columns in the output.
Up, PgUp: The Up arrow key moves a single line while PgUp scrolls the entire window. Down, PgDn: The Down arrow key moves a single line while PgDn scrolls the entire window. Left, Right: Move the view of displayable fields horizontally one column at a time. Home: Reposition the display to the un-scrolled coordinates. End: Reposition the display to the last displayable field or last task.
This is the end of our tutorial on top command examples in the Linux system. We hope you will be now able to view the Linux processes using the top command. If you still have any confusion, use the comment section below to ask the questions.